Heatable hoses have been fabricated for incorporation in many different end uses. For example, they can be used in hot melt adhesive applications to transport hot adhesive. They can also be used to transport hot gases to exit stacks without cooling the exit gas to below the dew point. Depending on the end-use requirements of these hoses, a variety of central tubes have been used in the past to make the hoses. Commonly, the central tube is made of a metal, such as stainless steel, providing the hose with a great deal of strength and chemical resistance. However, hoses having metal tubes, while readily available and reasonably inexpensive, are heavy and not very flexible.
Heatable hoses with polymeric tubes are also known in the art. The polymeric tubes commonly used in heatable hoses are fluoropolymers such as polytetrafluoroethylene (PTFE), a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) (PFA) or fluorinated ethylene propylene (FEP). These fluoropolymers are heat stable and exhibit lower weight per unit length for a certain thickness tube than a comparable metal tube. Fluoropolymer tubes are also relatively flexible when compared to metal tubes of comparable sizes and shapes. However, hoses containing fluoropolymer tubes typically do not possess as high strength as comparable hose containing a metal tube. This is of concern if the hose is of an extended length and is required to support its own weight. The strength of the fluoropolymer tube may be adversely effected by temperatures at which the hose may be heated. Also, fluoropolymer tubes exhibit a measure of permeation to certain gases, particularly acid gases such as NO.sub.x and SO.sub.x. This is of concern when a hose containing a fluoropolymer tube is part of a gas sampling device attached to a emitting stack for the detection and measurement of acid gases.
It would be desirable to have a flexible heatable hose comprising a polymeric tube that is relatively light, relatively strong, relatively flexible and is relatively impermeable to many acid gases, even at elevated temperatures.